Spectroscopic characterisation of dimeric oxidation products of phytosterols

Sterol dimers are the main oxidation products formed during sterols degradation at elevated temperatures. An investigation was carried out to decipher the structure of dimers differing in polarity, formed during β-sitosterol thermo-oxidation. The oxidation products were fractionated using silica gel into non-polar (NP), mid-polar (MP) and polar fractions (P). Oligomers were further separated by size-exclusion chromatography (SEC). Tentative chemical structures of non-polar, mid-polar and polar dimers were identified using Ag+/CIS–MS and APCI–MS procedures after on-line RP-HPLC separation. Further structures were verified by NMR and FT-IR spectroscopies.